Browsing by Author "Rogne, Otto"

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    Kinetic analysis of deuteron-transfer reactions of alkylamidines with [2H2]-4-nitrophenylnitromethane. Implications of isotopic scrambling for the determination of kinetic isotope effects
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Blanch, Jan H.; Rogne, Otto
    The kinetics of the deuteron transfer reactions of [2H2]-4-nitrophenylnitromethane with N,N-diethyl-n-butylamidine in toluene has been studied. The reaction is, in contrast to the corresponding proton transfer, kinetically complex, making it impossible to obtain accurate values for the deuteron transfer rate constant and hence for the isotope effect. The kinetic behaviour can be accounted for by a reaction mechanism involving H–D exchange between the acid and the base. This latter mechanism approaches equilibrium slower than the one-step process of the corresponding proton transfer. Theoretical runs calculated from the H–D exchange scheme fit the experimental data quantitatively if an isotopic rate ratio of about 14 is assumed.
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    Kinetic Isotope Effect in the Reaction of 4-Nitrophenyl- nitromethane with Pentamethylguanidine in Toluene
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Heggen, Inger; Lindstrøm, Jakob; Rogne, Otto
    Kinetic isotope effects have been determined for the proton-transfer and deuteron-transfer reactions of 4-nitrophenylnitromethane with pentamethylguanidine in toluene solution. The observed value of the isotopic rate ratio kHf/kDf at 25°C is 13.7 ± 0.4. The activation enthalpies are 2.4 ± 0.3 and 4.6 ± 0.3 kcal mol– 1 for the proton- and deuteron-transfer respectively. The results suggest a certain degree of tunnelling.
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    Kinetic Isotope Effect in the Reaction of 4-Nitrophenylnitromethane with the Cyclic Amidine Base DBU [l,5-diazabicyclo(5,4,0)undec-5-ene]
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Caldin, Edward F.; Rogne, Otto
    Kinetic deuterium isotope effects have been determined for the reaction of the cyclic amidine base DBU [1,5-diazabicyclo(5,4,0)undec-5-ene] with the carbon acid 4-nitrophenylnitromethane in toluene solution from –5 to +25°C. The isotopic rate ratio for the forward reaction (kHf/kDf) at 25°C is 13.3 ± 1.2; this is large enough to suggest an appreciable tunnelling correction. The activation enthalpies are strikingly low, both for proton and deuteron transfer: ΔH‡Hf= 2.0 ± 0.2 kcal mol–1(8.4 ± 0.8 kJ mol–1) and ΔH‡Df= 3.6 ± 0.3 kcal mol–1(15.1 ± 1.3 kJ mol–1). The interpretation of these results is discussed.
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    Kinetic Isotope Effects in the Reactions of 4-Nitrophenylnitromethane with Alkylamidine Bases in Toluene
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Caldin, Edward F.; Rogne, Otto; Wilson, Christopher J.
    Kinetic isotope effects have been determined for the proton-transfer and deuteron-transfer reactions of 4-nitrophenylnitromethane (4-NPNM; NO2C6H4CH2NO2, NO2C6H4CD2NO2) with two alkylamidine bases [HN = C(NEt2)R; R = n-butyl, n-nonyl] in toluene solution. The observed values of the isotopic rate ratio kHf/kDf at 25°C are 11.7 ± 1.0 and 8.0 ± 0.3, respectively. The former value indicates an appreciable tunnel correction; this is confirmed by a value of (ΔH[graphic omitted]D-ΔH[graphic omitted]H)= 2.5 ± 0.8 kcal mol–1(10 ± 3 kJ mol–1). The isotopic differences are not precise enough to allow calculations of the dimensions of the energy barrier.